The present invention relates to a method for making polyester carbonates. More particularly, the present invention relates to a melt condensation polymerization method involving the reaction of an aromatic dihydroxy compound, carbonic acid diester, and catalyst with a diacid.
Polyester carbonates and methods for their preparation have been studied extensively throughout the years. Polyester carbonates are thermoplastic resins that are clear and have high impact resistance. Due to their optical clarity and physical properties, polyester carbonates are used extensively in injection molding applications. The synthetic methods commonly used to made polyester carbonates are interfacial polymerization and melt condensation polymerization.
Interfacial polymerization is a well-known process. Fontana et al., U.S. Pat. No. 4,983,706, discuss the reaction of an aromatic dihydroxy compound such as bisphenol-A with phosgene and a diacid. The diacid is incorporated into the reaction mixture to produce a polyester carbonate melt flow such that the polyester carbonate is suitable for purposes of injection molding. Melt flow can also be described in terms of viscosity. Although the polyester carbonate produced by the interfacial method provides excellent viscosity for injection molding purposes, particulate contamination is often a problem. Additionally, the interfacial method uses a hazardous chemical, phosgene, and an environmentally hazardous chlorinated solvent.
Melt condensation polymerization is a known synthetic process which often results in less particulates found in the polymer compared to the interfacial method. Although melt condensation polymerization does not involve hazardous chemicals, the polyester carbonates made by the melt condensation polymerization process often do not have the flow properties of polyester carbonate made by the interfacial method.
In order to improve the flow properties of polyester carbonates made by the melt condensation polymerization process, different methods have been studied. Sakashitaet al. (Japanese Patent No. Hei 4[1992]-345616) discuss amethod for preparing polyester carbonates which incorporates aliphatic diacids directly into the polyester carbonate using a melt polymerization process. Sakashita et al. are concerned with polyester carbonates which incorporate the aromatic dihydroxy compound, 2,2,2',2'-tetrahydro-3,3,3',3'-tetramethyl- 1,1'-spirobi[1H-indene]-6,6'-diol, commonly known as SBI. In particular, Sakashita et al. are concerned with producing a polyester carbonate with a glass transition temperature greater than 100.degree. C. In addition, this method involves the use of a cocatalyst, boric acid, to facilitate the incorporation of aliphatic diacids directly into polycarbonate via a melt process.
In co-pending U.S. application, Ser. No. 09/431,277, a method is described which involves the pre-reaction of a diacid, carbonic acid diester and catalyst wherein a diester is formed. An aromatic dihydroxy compound is then added to the pre-reaction mixture in order to form a polyester carbonate. Said application discusses a method which involves the presence of a pre-reactor to initially convert the diacid and carbonic acid diester into a new diester for subsequent conversion into a polyester carbonate. The addition of a diacid successfully improves the flow properties of the polyester carbonate formed, yet requires the presence of a pre-reactor in the melt condensation polymerization process.
An efficient method which does not require the pre-reaction of the diacid with carbonic acid diester has yet to be developed.